1. Technical Field
The present invention relates to a vibration element, and a vibrator, an oscillator, an electronic apparatus, and a moving object each provided with the vibration element.
2. Related Art
An AT-cut quartz crystal vibrator for exciting a thickness-shear vibration as a principal vibration mode is suitable for miniaturization and high frequency. The AT-cut quartz crystal vibrator also has a frequency-temperature characteristic showing an excellent cubic curve. In view of the foregoing, an AT-cut quartz crystal vibrator is used in a variety of fields such as oscillators and electronic apparatuses. In particular, in recent years, due to the increase in processing speed of transmission communication equipment and OA equipment, or the increase in communication data capacity and processing amounts, a demand for increasing the frequency to the AT-cut quartz crystal vibrator used as a reference frequency signal source is increasing. One known technique for achieving a higher-frequency vibration is by decreasing the thickness of the vibrating part vibrating in the thickness-shear vibration mode.
JP-A-2012-253630 discloses an AT-cut quartz crystal vibration element which achieves a high-frequency vibration using an inverted-mesa structure having a thin-wall vibrating section and a thick-wall section disposed throughout the entire circumference of the outer edge of the vibrating section. This AT-cut quartz crystal vibration element includes a pair of excitation electrodes respectively disposed on a first principal surface and a second principal surface of the vibrating section in an opposed relationship to each other. Further, a pair of extraction electrodes extend from the respective excitation electrodes. In a plan view (also referred to as “the planar view”) of the vibration element, the pair of excitation electrodes have different sizes, and the larger excitation electrode entirely overlaps the smaller excitation electrode.
Since the vibration element described in JP-A-2012-253630 has an area where the extraction electrode extending from the smaller excitation electrode and the extraction electrode extending from the larger excitation electrode overlap each other, there is a possibility that this area may function as a vibration area in addition to the vibration area sandwiched by the pair of excitation electrodes. This may cause an unwanted spurious frequency near the resonant frequency.